As an alternative to the viscose process, in recent years there has been described a number of processes wherein cellulose, without forming a derivative, is dissolved in an organic solvent, a combination of an organic solvent and an inorganic salt, or in aqueous saline solutions. Cellulose fibres made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibres) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent", BISFA understands a mixture of an organic chemical and water. "solvent-spinning" means dissolving and spinning without derivatisation.
So far, however, only one process for the production of a cellulose fibre of the Lyocell type has achieved industrial-scale realization. In this process N-methylmorpholine-N-oxide (NMMO) is used as a solvent. Such a process is described e.g. in U.S. Pat. No. 4,246,221 and provides fibres having a high tensile strength, a high wet-modulus and a high loop strength.
However, the usefulness of plane fibre assemblies such as fabrics produced from the above fibres is significantly restricted by the pronounced tendency of the fibres to fibrillate when wet. Fibrillation means breaking off of the wet fibre in longitudinal direction at mechanical stress, so that the fibre gets hairy, furry. A fabric made from these fibres and dyed significantly loses colour intensity as it is washed several times. Additionally, light stripes are formed at abrasion and crease edges. The reason for fibrillation may be that the fibres consist of fibrils arranged in fibre direction, and that there is only little crosslinking between these.
WO 92/14871 describes a process for the production of a fibre having a reduced tendency to fibrillation. This is achieved by providing all the baths with which the fibre is contacted before the first drying with a maximum pH value of 8.5.
WO 92/07124 also describes a process for the production of a fibre having a reduced tendency to fibrillation, according to which the never dried fibre is treated with a cationic polymer. As such a polymer, a polymer having imidazole and azetidine groups is indicated. Additionally, a treatment with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or a crosslinking with glyoxal may be carried out.
In the lecture "Spinning of fibres through the N-methylmorpholine-N-oxide process", held by S. A. Mortimer and A. Peguy at the CELLUCON conference 1993 in Lund, Sweden, published in "Cellulose and cellulose derivatives: Physico-chemical aspects and industrial applications" edited by J. F. Kennedy, G. O. Phillips and P-O. Williams, Woodhead Publishing Ltd., Cambridge, England, pp. 561-567, it was mentioned that the tendency to fibrillation rises as drawing is increased.
From the lecture "Besonderheiten des im TITK entwickelten Aminoxidprozesses" held by Ch. Michels, R. Maron and E. Taeger at the symposium "Alternative Cellulose--Herstellen, Verformen, Eigenschaften" at Rudolstadt, Germany, in September 1994, published in Lenzinger Berichte September, 1994, pp. 57-60, it is known that there is a relation between the filament tension in the air gap and the mechanical properties of the fibrous materials. At the same symposium, P. Weigel, J. Gensrich and H.-P. Fink mentioned in their lecture "Strukturbildung von Cellulosefasern aus Aminoxidlosungen", published in Lenzinger Berichte September, 1984, pp. 31-36, that the fibre properties may be improved when the filaments are dried without simultaneously exposing them to a tensile stress.
In DE-A-42 19 658 and EP-A-0 574 870 it is described that post-drawing of the precipitated filaments has a negative effect on the textile properties of the fibres, particularly on their elongation.
From WO 96/18760 cellulose filaments are known which exhibit a strength of 50 to 80 cN/tex, a breaking elongation of 6 to 25% and a specific tear time of at least 300 s/tex. During production these filaments are exposed to a tension in the range of 5 to 93 cN/tex. It is disclosed that these fibres exhibit a low tendency to fibrillation.